Manky's Pop.

[tbone]

So your not getting enough stroke in the master cyl to supply enough fluid at the right pressure through both outlets to the servo?
Cant be right, because the 2 circuits operate independently of each other within the same body.

But if you only use 1 outlet and that fails.....no brakes!

[terry t]

So your not getting enough stroke in the master cyl to supply enough fluid at the right pressure through both outlets to the servo?
Cant be right, because the 2 circuits operate independently of each other within the same body.

But if you only use 1 outlet and that fails.....no brakes!

Tim i think were all missing the point.no offence but the way i read this now is
this servo is a twin servo.dual circuit . so is the fail safe system built in the servo so you dint need the dual circuit master cylinder. there saying use one as it a bigger bore cylinder but don't need the dual part
so one pipe from master cylinder to servo with a tee piece for the two inlets.

[tbone]

Hi guys.
Thanks for your input. Two things that mean absolutely nothing to me at all -brakes & electrics. Never understood them. That's why I called in outside help in both areas. Terry's doing a crackin' job on the wiring & I trust Kev entirely with the brakes. I really don't know where we go from here, just seem to be going round in circles, but as Kev says, we need to attack it in an orderly, progressive way, eliminating one thing at a time.
To be honest, I'm just about ready to chuck it all in. Been living under the threat of deadlines for months now & all I think about all day is this bloody truck. The fun's gone out of this build completely & it's just become an ordeal. I'm spending more time at Loony's workshop than I am at home.
I should be there now, working on the gearbox tunnel, but it's a gorgeous sunny Sunday morning here & I need a break. I'm taking a day off to go outside & enjoy the sunshine.

Means nothing to me either, but its easier to sit here n throw some ideas around than it is to actualy be doing the work  

When`s the deadline Andy?

[tbone]

So your not getting enough stroke in the master cyl to supply enough fluid at the right pressure through both outlets to the servo?
Cant be right, because the 2 circuits operate independently of each other within the same body.

But if you only use 1 outlet and that fails.....no brakes!

Tim i think were all missing the point.no offence but the way i read this now is
this servo is a twin servo.dual circuit . so is the fail safe system built in the servo so you dint need the dual circuit master cylinder. there saying use one as it a bigger bore cylinder but don't need the dual part
so onepipe from master cylinder to servo with a tee piece for the two inlets.

That`s how i read it too Terry, but I can`t see there is a built in failsafe, after all, you will only be relying on a single input from the master cylinder.
The reason for the duel circuit is as we know, that if one fails, the other is still operational. Use only one circuit, and if that fails.....no pressure at the servo...no brake.

[Manky Monkey]

Final, final deadline is the 9th of April. Haven't booked the re-test yet, but aiming for maybe the week starting the 5th March, (week after next).

[kapri]

So your not getting enough stroke in the master cyl to supply enough fluid at the right pressure through both outlets to the servo?
Cant be right, because the 2 circuits operate independently of each other within the same body.

But if you only use 1 outlet and that fails.....no brakes!

Tim i think were all missing the point.no offence but the way i read this now is
this servo is a twin servo.dual circuit . so is the fail safe system built in the servo so you dint need the dual circuit master cylinder. there saying use one as it a bigger bore cylinder but don't need the dual part
so one pipe from master cylinder to servo with a tee piece for the two inlets.

You need a twin master cylinder otherwise it is still single circuit . On a standard singel circuit you use one servo ie m/c to servo and then split to front and rear. Think of this as two seperate servos mounted close together with one servo feeding rear brakes and one feeding front. You can see you now need two seperate inputs as the servos are totally indepent internally.

[kapri]

M/c is correct size for system ,increased from previous bore as supplied with wrong info re rear axle /front brake source initially. Convinced the excessive travel is down to trapped air .

[tbone]

M/c is correct size for system ,increased from previous bore as supplied with wrong info re rear axle /front brake source initially. Convinced the excessive travel is down to trapped air .

Me too.....either in the servo unit or the master cylinder. Bleed the servo has to be first on the list.

Just spoken with Terry and can understand his logic if the master cylinder is just a duel outlet and not a duel circuit.

[terry t]

if its trapped air why is the front wheels locked on

[tbone]

The front residual valves.....ditch them.

[Manky Monkey]

I'll pester Loony to give me a hand to bleed the servo tomorrow afternoon. As luck would have it, just when things are getting tight, Loony's become busier in the paintshop than ever before. No bad thing -unless you have a deadline to meet.  
The 2 servo bleed nipples are the highest in the system, so to my simple monkey mind, would be the logical point for trapped wind, air to be.

I'd just like to publicly point out, I have the utmost faith in Kev's abilities & experience. I'm not questioning his work at all. I'm a life-long biker, not a car builder & have no idea what's going on here. Everything seems a million times more complicated than I've ever dealt with before. The test deadline's piling pressure onto what's already a major headache.

[ByzMax]

I could be  wrong but as far as I remember a dual master cylinder should be piped diagonally not seperated front to back.

You should have one front and the opposite side rear attached to each output

I don't know if that affects your problem just an observation.

I'm aware that with your brake setup and residual valves etc this may not be possible.



The servo should be bled.

If you are bleeding the system by hand/foot your probably gonna have air stuck in it at a high point and as stated by Tbone angle the servo so the air is not trapped and trying to go back to the high point.

Get it power bled.

If the callipers are sticking on then they are either stuck or the pressure is being maintained.

So with the caliper stuck, open one of the bleed nipples. Does it back off?

Yes? Then you know you have something maintaining the pressure.

Bypass the residual valve and test to see if that is the problem

NO ? Then the calliper is sticking.

Clear this fault first.

Then Bleed the system.

If the system still has to be pumped then bypass the servo and try again and then look at the master cylinder.

As stated by others

Keep it simple and only make one change at a time and then test it.

Hope that helps


 

[terry t]

Were not questioning Kev. were all trying to sort out were missing some thing and an answer will come
but the info about the master cylinder and servo is from a vw specialist and were using vw cylinder.
Kev has said that he hasn't had any dealings with this servo. its all built in twin circuits

[terry t]

I could be  wrong but as far as I remember a dual master cylinder should be piped diagonally not seperated front to back.

You should have one front and the opposite side rear attached to each output

I don't know if that affects your problem just an observation.

I'm aware that with your brake setup and residual valves etc this may not be possible.



The servo should be bled.

If you are bleeding the system by hand/foot your probably gonna have air stuck in it at a high point and as stated by Tbone angle the servo so the air is not trapped and trying to go back to the high point.

Get it power bled.

If the callipers are sticking on then they are either stuck or the pressure is being maintained.

So with the caliper stuck, open one of the bleed nipples. Does it back off?

Yes? Then you know you have something maintaining the pressure.

Bypass the residual valve and test to see if that is the problem

NO ? Then the calliper is sticking.

Clear this fault first.

Then Bleed the system.

If the system still has to be pumped then bypass the servo and try again and then look at the master cylinder.

As stated by others

Keep it simple and only make one change at a time and then test it.

Hope that helps


 

Iain they release when you crack open the bleed nipple on the front

[Manky Monkey]

The servo mounts horizontally, with the brake pipes entering at either end & the bleed nipples on the top, so it can't be angled in any way really.
I'm told dual circuit brakes were originally plumbed front & back, then they changed to diagonal, then back to front & back again.